os.execute ([command]) This function is equivalent to the ISO C function system. It passes command to be executed by an operating system shell. Its first result is true if the command terminated successfully, or nil otherwise. After this first result the function returns a string plus a number, as follows: "exit": the command terminated normally; the following number is the exit status of the command. "signal": the command was terminated by a signal; the following number is the signal t

os.difftime (t2, t1) Returns the difference, in seconds, from time t1 to time t2 (where the times are values returned by os.time). In POSIX, Windows, and some other systems, this value is exactly t2-t1.

os.date ([format [, time]]) Returns a string or a table containing date and time, formatted according to the given string format. If the time argument is present, this is the time to be formatted (see the os.time function for a description of this value). Otherwise, date formats the current time. If format starts with '!', then the date is formatted in Coordinated Universal Time. After this optional character, if format is the string "*t", then date returns a table with the following fiel

os.clock () Returns an approximation of the amount in seconds of CPU time used by the program.

next (table [, index]) Allows a program to traverse all fields of a table. Its first argument is a table and its second argument is an index in this table. next returns the next index of the table and its associated value. When called with nil as its second argument, next returns an initial index and its associated value. When called with the last index, or with nil in an empty table, next returns nil. If the second argument is absent, then it is interpreted as nil. In particular, you can use

math.ult (m, n) Returns a boolean, true if and only if integer m is below integer n when they are compared as unsigned integers.

math.type (x) Returns "integer" if x is an integer, "float" if it is a float, or nil if x is not a number.

math.tointeger (x) If the value x is convertible to an integer, returns that integer. Otherwise, returns nil.

math.tan (x) Returns the tangent of x (assumed to be in radians).

math.sqrt (x) Returns the square root of x. (You can also use the expression x^0.5 to compute this value.)